The present invention relates to an ultraviolet detecting device using photodiodes that produces currents in light and its manufacturing method, and an ultraviolet quantity measuring apparatus.
In a conventional ultraviolet receiving or detecting device, photodiodes laterally disposed opposite to each other in such a manner that comb teeth portions of both an N+ diffusion layer in which an N-type impurity is diffused in a high concentration and which is shaped in the form of an “E”-shaped comb type, and a P+ diffusion layer in which a P-type impurity is diffused in a high concentration and which is shaped in the form of “π”-shaped comb type, are brought into engagement with each other, are formed in a silicon semiconductor layer with an N-type impurity diffused therein in a low concentration, of a semiconductor wafer of SOI (Silicon On Insulator) structure in which a silicon semiconductor layer of an about 150 nm-thick is formed on a silicon substrate with an embedded oxide film interposed therebetween. A predetermined voltage is applied to wirings electrically connected to the N+ diffusion layer and the P+ diffusion layer to detect the intensity of ultraviolet light (refer to, for example, a patent document 1 [Japanese Unexamined Patent Publication No. Hei 7(1995)-162024 (paragraph 0025 in 4th page—paragraph 0035 in 5th page, FIG. 2 and FIG. 3)]).
With an increase in the exposure dose of ultraviolet light or rays due to destruction of the ozone layer, there has been a growing concern about the influence of ultraviolet light or rays contained in the sunlight on a human body and environments.
In general, the ultraviolet light or rays mean light invisible in an ultraviolet region or range of 400 nm or less in wavelength. The ultraviolet rays are classified into long wave ultraviolet light (UV-A wave: about 320 nm to 400 nm in wavelength), medium wave ultraviolet light (UV-B wave: about 280 nm to 320 nm in wavelength) and short wave ultraviolet light (UV-C wave: about 280 nm or less in wavelength). Influences exerted on the human body and environments differ depending on their wavelength regions or ranges. The UV-A wave causes skin to darken and reaches the inner or true skin, thus resulting in aging. The UV-B wave causes skin irritation and is in danger of inducing skin cancer. The UV-C wave will produce strong bactericidal action. The UV-C wave is however absorbed into the ozone layer and does not reach the ground.
Promptly notifying a daily exposure dose of ultraviolet light presents an important challenge in terms of human-body protection. An UV index that gives an indication of the quantity of ultraviolet light has been introduced in 1995. A recommendation has been made to announce this value together with a weather forecast or the like through mass media.
Such an UV index can be calculated using the CIE action spectrum defined by CIE (Commission Internationale de I'Eclairage) as the relative degree of influence on the human body. The photo-detection characteristic of a UV-B wave strong in the degree of influence on the human body is multiplied by the action spectrum every wavelength. The so-resultant ones are integrated in a wavelength range of the UV-B wave, so that the corresponding UV index can be calculated.
Therefore, there has been growing expectations for development of such a sensor as to separate ultraviolet light or rays lying in two wavelength ranges of UV-A and UV-B waves and detect their intensities.
The prior art referred to above has however a problem in that although the total quantity of ultraviolet light lying in an ultraviolet region or range of 400 nm or less in wavelength can be detected, the two wavelength ranges cannot be detected in separated form.